Journal Club

Highlighting recently published papers selected by Academy members

One example of how the Maya modified their environs: They cleared large tracts of forest in and around the city of Tikal, located in present-day Guatemala. Image: Shutterstock/Simon Dannhauer

The ancient Maya once had a civilization in the Americas that stretched over an area the size of Texas. Now scientists detail a number of key ways the Maya left behind a lasting impact on the environment during the so-called “Mayacene.”

Located in what is now southern Mexico and northern Central America, the Classic Maya civilization lasted from about 250 to 900 AD and had a population of roughly several million people, potentially rivaling the population density of medieval Europe (though precise population estimates are still a matter of debate).

The epoch defined by the human influence on Earth’s ecosystems and environment is often called the Anthropocene. Lead author Tim Beach and his colleagues suggest the Maya reshaped the Earth enough to leave behind a chapter within the Anthropocene that they call Mayacene. In the Sept. 15 issue of Quaternary Science Reviews, the scientists detailed various discoveries, including their own, related to myriad Maya impacts.

Analysis of soils, lakes, floodplains, wetlands and other ecosystems in Central America has unearthed evidence for Maya impacts on climate, vegetation, hydrology and the lithosphere. This led Beach, a soil geomorphologist and geoarchaeologist at the University of Texas at Austin, and his colleagues to believe that the Mayacene lasted from about 3,000 to 1,000 years ago. “Both the Mayacene and Anthropocene recognize the fact that human impacts on the planet are as substantive as the impacts of natural forces on the planet,” says Tom Guderjan, director of the Maya Research Program.

The ancient Maya altered the environment with vast urban and rural infrastructure. These included thousands of reservoirs, dams, canals, terraces, ditches and wells to help them deal with floods and droughts during wet and dry seasons, as well as limestone quarries to help construct multiple pyramids and other stone buildings.

There is abundant evidence that the Maya also had impacts on their forests — for instance, useful species such as beans, squash, corn, manioc, avocado, cacao and guava appear to have dominated ancient remains of orchards and fields. Still, even at the large Maya city of Tikal, as much as 40 percent of the forest may have remained intact during the height of the civilization, leading to a kind of “garden city,” Beach and his colleagues note.

“Keeping some forests would have allowed for things like hunting and firewood,” says Guderjan, adding that the amount of foresting in ancient Tikal is a matter of debate. “And it takes a lot of work to keep 100 percent of the forest out.”

The scientists paid special attention to ancient soils or “paleosols” that possess chemical signs of human occupation. For example, human activity such as cooking and waste disposal concentrates phosphorus and other nutrient elements in the soil, and phosphorus often forms compounds that can persist for millennia.

Carbon isotope ratios are another marker. Different plants depend on different types of photosynthesis, which prefer different carbon isotopes. By analyzing the ratios of these different carbon isotopes within soils, Beach and his team could infer what plants once dominated areas, whether indicative of agricultural crops or tropical forest.

Echoing present-day climate concerns, the authors note that the Maya’s widespread deforestation and wetland farming could have influenced climate factors such as the degree to which the ground reflects sunlight, or atmospheric levels of greenhouse gases, dust and water.

Beach and his colleagues now plan to use Lidar (a remote sensing method that employs lasers) to scan through forest canopies. “We think we have yet to find and study the biggest wetland field complexes,” Beach says.

“Thinking about the Mayacene can bring us down some new research directions,” Guderjan says. “How did people utilize what was there and irrevocably change what was there?”